Continuing Fire Regimes in Remote Forests of Grand National Park

Peter Z. Fulé Thomas A. Heinlein W. Wallace Covington Margaret M. Moore

Abstract—Ponderosa forests in which frequent fire regimes Kaibab . It took another 78 years before the first continue up to the present would be invaluable points of reference European settlement was begun by Mormon explorers and for assessing natural ecological attributes. A few remote forests on pioneers in 1854. Fighting with Utes and Navajos kept the North Rim of National Park come close to this settlers out of the Strip until 1869. With the ideal: never-harvested, distant from human communities and fire establishment of peace, there was a rapid expansion of suppression resources, and with several low-intensity fires in the livestock grazing, logging and mining activity. past century—a highly unusual recent fire regime in the Southwest. Frequent fire regimes were disrupted in forested high- Recent fires appear to have played a crucial role in preventing the lands of the as early as 1870 in the Mt increases in forest density that characterize most southwestern Trumbull area (Fulé and others, unpublished data). As pine forests. The study sites are not unaffected by the ecological elsewhere in the Southwest, early livestock grazing was changes associated with settlement, but they do present an impor- excessive (Altshul and Fairley 1989) and removed fine tant reference resource for study and management of ponderosa herbaceous fuels, stopping fire spread. The establishment pine ecosystems. of the Grand Canyon Forest Reserve in 1893 and creation of Grand Canyon National Park (GCNP) in 1919 brought organized fire detection and suppression crews. On the North Rim, Wolf and Mast (1998) found complete fire Ponderosa pine forests in which historically frequent fire exclusion by about 1920 in ponderosa pine and mixed regimes continue up to the present would be invaluable forests. Even in the high-elevation spruce- for- points of reference for assessing natural attributes of eco- ests, with historically longer fire-return intervals and more logical structure and function. Grand Canyon National Park severe fires, protracted fire exclusion has led to the devel- contains one of the largest old-growth forests in the South- opment of increasingly dense, homogeneous stands (White west, where tree harvesting has not occurred and grazing and Vankat 1993). Park management policy has changed has been eliminated for over 60 years. Although most fire in recent decades to favor restoration of natural ecological disturbance regimes in the park have been disrupted since processes, including fire (GCNP 1992), but the presently European settlement, a few remote sites may retain near- dense forests and heavy fuel loads hinder effective re- natural conditions. The majority of the forested area lies on introduction of fire on much of the North Rim. Fuel prob- the North Rim, part of the , which supports lems are not only an ecological concern: the difficulty of fire ponderosa pine, mixed conifer and spruce-fir forests at management on the North Rim has been cited by Pyne elevations ranging from 7,500 to 9,165 feet on well-drained (1989) as a major factor impeding the Park’s plan for . wilderness designation of the area (Morehouse 1996). The North Rim is remote from modern human communi- Among the challenges faced by managers are: 1) lack of ties, but Altshul and Fairley (1989) document the long knowledge about natural ecological conditions as a point of human history of the . The lower elevations of the reference for restorative management (Moore and others rim were densely populated by Native Americans prior to 1999), 2) uncertainty about the appropriate mix of pre- 1250-1300 A.D. Six tribes—the Paiute, Hopi, Havasupai, scribed fire and tree thinning for treating accumulated Hualapai, Navajo, and Zuni—have ancestral and current fuels (Nichols and others 1994), and 3) a host of off-site connections to the canyon and rim . An expedition issues including air quality, developing management pro- led by the Spaniards Dominguez and Escalante in 1776 cedures suitable for wilderness areas and working in a marked the first European presence on the Arizona Strip, highly charged political environment. the land north of the that includes the Our study focuses on the first of these questions: charac- terizing fire regimes on several sites that may be among the least impacted by recent fire exclusion in the Southwest. The northwestern points and of the North Rim In: Cole, David N.; McCool, Stephen F.; Borrie, William T.; O’Loughlin, Jennifer, comps. 2000. Wilderness science in a time of change conference— have the most frequent lightning ignitions in the Park Volume 5: Wilderness ecosystems, threats, and management; 1999 May 23– (GCNP fire records). As part of a broader study on fire and 27; Missoula, MT. Proceedings RMRS-P-15-VOL-5. Ogden, UT: U.S. Depart- ment of , Forest Service, Rocky Research Station. forest structure in the Park, we selected three representa- Peter Z. Fulé is Assistant Research Professor, Thomas A. Heinlein is tive sites: , a mesa separated from the Research Specialist, W. Wallace Covington is Regents’ Professor, and Marga- Kaibab Plateau “mainland,” Fire Point, the westernmost ret M. Moore is Professor, School of Forestry, Universiy, Flagstaff, AZ 86011 U.S.A. extension of the rim, and Rainbow Plateau, a peninsula to

242 USDA Forest Service Proceedings RMRS-P-15-VOL-5. 2000 the southeast (fig. 1). The forests are dominated by old average January minimum of 30° F (GCNP1992; White trees, with lush understory vegetation and substantial and Vankat 1993). Vegetation includes ponderosa pine evidence of recent fires. The sites are not without recent (Pinus ponderosa), Gambel (Quercus gambelli), and human impact: these areas were grazed prior to construc- New Mexican locust (Robinia neomexicana) trees, with an tion of the North Rim boundary fence in 1938 (Schroeder, understory of forbs and perennial grasses (Bennett 1974). personal commnication) and fire suppression was practiced Fire-scarred tree sampling was done in June-July, 1998. here through much of the 20th century (Pyne 1989). How- Partial cross-sections were cut from scarred “catfaces” on ever, we anticipated that the limited water for livestock and trees, logs, and stumps of that appeared to repre- difficult access for firefighters might have minimized dis- sent the oldest and/or most extensive fire records. Samples ruption of the fire regime. Our goals were to quantify the fire were mapped when collected and were well-distributed regime, describe any post-settlement changes and assess throughout the study areas. In the lab, samples were management implications. mounted, surfaced with progressively finer sandpaper and crossdated (Stokes and Smiley 1968) using characteristic patterns of narrow marker years: 1722, 29, 35, 48, 52, 72, 82 Methods ______(false ring), 1810, 13, 20, 22, 45, 47, 73, 79, 96, 99, 1902, 04, 51, 63, 77, 96. All dates were independently confirmed by The study sites totaled nearly 1,700 acres. The Powell another dendrochronologist. The season of fire occurrence Plateau site covered 780 acres, ranging from 7,400 to 7,660 (Baisan and Swetnam 1990) was estimated from the relative feet in elevation. The Fire Point site was 333 acres, 7,570 to position of each fire lesion within the annual ring. 7,770 feet in elevation. The Rainbow Plateau site was 550 Fire history data were analyzed with the FHX2 software acres, 7,550 to 7,658 feet in elevation. Soils have not been (Grissino-Mayer 1995). Analysis at each site began with the mapped in detail for these sites, but North Rim soils in first year with an adequate sample depth (Grissino-Mayer general are predominantly of the Soldier series, derived and others 1994). Fire return intervals were analyzed statis- from . Average annual on the tically in different categories related to the size and/or North Rim is 23 inches, with an average annual snowfall of intensity of past fires. The fire data were filtered to look at 129 inches. Temperatures are cooler than on the South Rim, progressively greater proportional scarring as a proxy for ranging from an average July maximum of 79° F to an

Figure 1—Study sites on the North Rim of Grand Canyon National Park.

USDA Forest Service Proceedings RMRS-P-15-VOL-5. 2000 243 fire size (Swetnam and Baisan 1996). First, all fire years, even America, we usually find sites with good records but no fires those represented by a single scar, were considered. Then, we (USA—Swetnam and Baisan 1996) or many fires but limited included only those fire years in which 10% or more, and 25% records (—Fulé and Covington 1997, 1999). The Grand or more, of the recording samples were scarred. The statisti- Canyon sites in the present study have both recent fires and cal analysis of fire return intervals includes several measures written historical data: fire records maintained at GCNP of central tendency: the mean fire interval (MFI, average since 1924 provide an unusual opportunity for a quantita- number of years between fires), the median and the Weibull tive test of the utility of fire scars in reconstructing the median probability interval (WMPI). temporal and spatial pattern of past fires. The relationship between climatic fluctuations and fire The fire record data were used with caution. The database occurrence was compared by superposed epoch analysis was patchy in the early years. Many recorded fire sizes and (SEA), using software developed by Grissino-Mayer (1995). geographic locations were considered approximate, and some A locally developed, ponderosa pine tree-ring chronology evident errors were observed, such as coordinates that served as a proxy for climate. The SEA superimposes fire placed fires well outside the Park’s boundaries. Nonethe- years and summarizes the climate variable (tree-ring width) less, the database was a valuable independent source of fire for fire years, as well as preceding and succeeding years. The history information. After completing the fire scar analysis output of the SEA was a comprehensive comparison of the without reference to the database, we selected records of climate, as represented by tree-ring width, for five years fires occurring in and around (within 1 km) the study sites before fire years, the fire years themselves, and two years for comparison with the fire scar data. after fire years. The degree to which the climate variable in each analysis year differed from the average climate was assessed with 90%, 95%, and 99% confidence intervals, Results and Discussion ______developed using bootstrapping methods, with 1,000 simula- tions based on random windows with the actual fire events Fire Regimes (Grissino-Mayer 1995). Composite fire history graphs for all fires on all three sites Accuracy of the fire scar record could be tested because a show that fires were frequent through 1879 and fires contin- relatively high number of fires occurred on the study sites in ued to occur sporadically up through the present (fig. 2). the 20th century, due both to the isolation of the sites and to Prior to 1879, the Weibull Median Probability Interval recent fire management policies. Across western North

Figure 2—Fire history results are summarized in these graphs, with each horizontal line representing the composite of all sampled trees on a site and the short vertical lines noting the year of fire occurrence. Fire regimes are compared in two categories: all fires, including even those which scarred only a single sample tree (top graph); and fires scarring 25% or more of the sample trees (bottom graph).

244 USDA Forest Service Proceedings RMRS-P-15-VOL-5. 2000 (WMPI) at Powell Plateau was less than three years, rising some portions of the Wildernesses have had repeated 20th to about 3.9 years on Rainbow Plateau (table 1). Considering century fires (Rollins and others, in press). only the 25%-scarred fires, the WMPI values were about two The timing of postsettlement fires may also be important. to three times higher, suggesting that small fires were more Regeneration flushes in the early 20th century, especially common than larger ones. The fire return intervals fall 1919, were important in forming dense forests in northern within the range of values reported at other southwestern Arizona (Savage and others 1996; Mast and others 1999). sites (Swetnam and Baisan 1996), close to the high fre- Large fires on Powell Plateau in 1892 and 1924, Fire Point in quency end of the distribution. These sites might have been 1923 and Rainbow Plateau in 1900 may have been instrumen- expected to have relatively infrequent fires, as did isolated tal in thinning seedlings. The other post-settlement fires were smaller mesas in , (Madany and all post-1980, reflecting the change in park policy toward West 1982), because the study sites are isolated high-eleva- prescribed natural fire. In light of the fire regime data, we will tion landmasses at the western edge of the canyon rim. The evaluate forest structural information from the same study prevailing southwestern tend to carry fire out of the sites to assess changes from reference conditions. sites, while the likelihood of importing fire from lower- elevation lands to the west seems low, due to the reduced chance of low-elevation lightning strikes and discontinuous Comparison to Fire Records fuels (although there is a chaparral belt extending for about Fire scars were highly accurate in identifying historic 1,000 feet below the rim). The fact that high fire frequencies fires: every fire on the study sites recorded since 1924 and were observed suggests that lightning densities are high on larger than 20 acres was identified from fire scars. The the study sites. Ignitions by Native Americans may have largest fire from written records missed in the fire-scar played a role as well (Schroeder, personal communication). reconstruction was a 20-acre prescribed natural fire on the The many synchronous fire dates in fig. 2 suggest that Rainbow Plateau in 1987. Many smaller fires, suppressed at presettlement fires spread between the study sites in many one acre or less in size, did not show up in the fire scar record. years, or that sites were ignited separately in the same The proportion of scarred trees was generally related to fire years. size. The greatest discrepancy between fire size and scarring Fires occurred primarily in dry years following wet years proportion occurred with the 1931 Fire Point fire, which (fig. 3), assuming that tree-ring widths in the local chronol- burned 160 acres but was recorded only on a single scarred ogy adequately reflect moisture varability. Similar patterns sample. In the case of this fire event, reliance on the 25%- were observed across the Southwest by Swetnam and scarred criterion would underestimate fire size. Betancourt (1990), who suggested that increased herba- Mapped fire perimeters from the Emerald prescribed ceous production in moist years led to high fuel loading and natural fire in 1993 matched well with fire scar data (fig. 4). continuity in subsequent years. The fire was recorded on only half of the 12 fire-scarred Clearly, fewer fires burned after 1879, especially using the samples collected from within its boundary, but the six 25%-scarred criterion that filters out the presumably smaller samples were well-distributed. Taking these six samples fires that scarred fewer samples (fig. 2). The question is, how and applying a reasonable spatial buffer of 1,000 feet around much disruption of the fire regime results in ecologically them would fairly closely approximate the geographic bound- significant changes? Each site has had either two or three ary and size of the Emerald fire. large fires since settlement. These post-settlement fires The close correspondence between the fire scar data and contrast with fire exclusion in the majority of forests in the the Park’s fire records builds confidence in the interpreta- Southwest (Swetnam and Baisan 1996). Fires were excluded tion of presettlement fire regime characteristics. While fire in most of the only other large unharvested southwestern scar methods do have limitations (Johnson and Gutsell ponderosa pine forest, ’s Gila/ Wil- 1994), our results suggest that the rationale described by derness Areas (Swetnam and Dieterich 1985), although Swetnam and Baisan (1996) for proper use of fire scar data,

Table 1—Fire return intervals at the study sites, in two categories: (1) all fire years, including even those represented by a single scarred sample, and (2) fire years in which 25% or more of the recording trees were scarred.

Weibull Median Mean fire Probability Site interval (MFI) Minimum Maximum Interval (WMPI) Powell – All 3.24 1 9 2.97 Powell – 25% 9.45 3 24 8.56

Fire Pt. – All 3.65 1 11 3.42 Fire Pt. – 25% 6.35 2 11 6.25

Rainbow – All 4.00 1 11 3.86 Rainbow – 25% 7.81 3 18 7.53

USDA Forest Service Proceedings RMRS-P-15-VOL-5. 2000 245 Figure 3—Relationship between local climate (tree-ring width index) and fire occurrence determined by superposed epoch analysis (SEA). The average climate value is scaled to one. Bootstrapping procedures were used to assess the statistical significance of climate departures above the mean (“wet years”) and below the mean (“dry years”) in the fire years (year 0), the five years preceding fires (-5 through –1), and the two year after fires (1-2). The three lines above and below the x-axis in each graph represent confidence intervals of 90%, 95%, and 99%.

filtering data according to the proportion of scarred samples, even though it is in precisely such years that large presettle- is sound. ment fires occurred. Current management policy is directed toward beneficial use of wildland fire for resource benefits, primarily applied Management Implications in ponderosa pine forests, where burning is less risky. In Presettlement fire regime data serve as a point of 1998, for example, a small lightning-ignited fire was inten- reference for ecosystem management, particularly in Park tionally expanded with aerial ignition over the Rainbow Service wildlands managed primarily for their natural Plateau. When fire use involves management ignitions, qualities. One logical course of action would be to permit park managers are faced with different questions. The fire natural ignitions to burn without impediment, using the behavior may be less hazardous, but the fire timing and reference fire regime data as a standard against which to spread will be controlled more by management than by fuel judge the effectiveness of fire restoration. and weather patterns. Fire use is unlikely to be permitted But if a natural fire policy were to be fully adopted, the during dry fire seasons, so fire timing and size would prob- Park would have to accept the occurrence of large fires ably remain outside the range of natural variability. Fire use spreading over thousands of acres, dropping below the rim may also pose conflicts with the Park’s wilderness proposal, and burning during the summer fire season. The biggest because fire managers rely on helicopters, vehicles, and fires, reaching well into the higher elevations of the Kaibab other equipment to carry out burns. Plateau, would most likely occur during the driest years. Smoke remains a significant management challenge at When these fires encountered the dense mixed conifer for- Grand Canyon because of the Class I airshed designation, ests above 8,000 feet elevation, intense fire behavior and the importance of scenic vistas for park visitors, and the severe fire effects would occur, in contrast to the effects of the active role taken by the Park in opposing other off-site frequent surface fires that prevailed prior to settlement pollution sources, such as power plants. (Wolf and Mast 1998). In the past decade, the two driest Despite the difficulties in restoring fire to the Park, there years in northern Arizona have been 1989 and 1996. The is no alternative: fuels will burn eventually. The question is 1989 Muav wildfire, ignited by lightning, was perceived as how best to intervene. An ecological restoration experiment a threat of such magnitude that the use of bulldozers was that tests thinning of small trees, as well as prescribed authorized in the Park to construct fireline. The 1996 fire burning (Covington and others 1997; Heinlein and others, in season was the worst on record in the Southwest, with the press), may offer management alternatives for some areas of 50,000 acre Bridger Complex fire burning just north of the the Park. Park boundary. Neither in 1989 nor in 1996 would park The resilience of forest ecosystems will be key to the eventual managers have been able to authorize natural fires to burn, restoration of natural processes. Although presettlement fire

246 USDA Forest Service Proceedings RMRS-P-15-VOL-5. 2000 D. Spotskey, M. Schroeder, J. Schroeder, K. Crumbo, N. Bryan, J. Balsam, R.V. Ward, A. Horn-Wilson and D. Bertolette. Northern Arizona University’s Ecological Resto- ration Program students and staff, especially J.P. Roccaforte, supported data collection and sample preparation. This work was funded by a grant from the U.S. Department of the Interior.

References ______

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